In a pulsed laser, light inside the laser circulates along an optical path. In many cases, a repetition rate or repetition frequency of the pulsed laser depends on the optical path length of the optical path. If the optical path length decreases or increases away from a specified value, the repetition rate of the pulsed laser can increase or decrease away from a specified value, which is undesirable.
Accordingly, there exists a need for improving the systems and methods for controlling the optical path length and/or the repetition frequency.